Thermostatic control for electron discharge devices



April 17, 1934. J H, PAYNE 1,955,560

THERMOSTATIC CONTROL FOR ELECTRON DISCHARGE DEVICES Filed May 29, 1931 TEMPERATURE OF GOA/025N660 MfRGl/RY VAPOR Q Inventor: John H.Payne, I0 .90 /00 AMBIENT TEMPfRATU/Rf/"C/ y 45 His Attorney.

Patented Apr. 17, 1934 UNITED STATES earl-2m OFFICE John H. Payne, Ballston Spa, N. Y., assignor to General Electric Company, a. corporation of New York Application May 29. 1931, Serial No. 541,083

My present invention relates to electric discharge apparatus, and more particularly to an accessory for maintaining the temperature of such devices relatively constant notwithstanding 5 variable temperature conditions surrounding the apparatus.

Electrical discharge devices which depend upon the ionization of vapor to carry large currents are useful as power rectifiers and relays. These devices ordinarily employ a thermionic cathode as a source of electrons, a cooperating anode and an electrostatic control member or grid, and a vapor which constitutes the ionizable medium. The pressure of the medium and the impressed voltages are such that a discharge of arc-like character is produced between the electrodes, the initiation of the discharge being controlled by the bias on the grid. After the arc is started, the grid loses control when ordinary and practical bias voltages are employed and can neither modulate, limit nor extinguish the arc under these conditions. The starting of the arc may be repeated indefinitely, for while the discharge can- P not ordinarily be extinguished by the grid, it can 20 be stopped by removing the anode voltage. Upon applying this voltage, the grid voltage can determine whether the arc will start and by a continued repetition of this process, the grid voltage can control the average anode current over a period of time. A practical method of obtaining interruption of the anode circuit is to employ alternating current or interrupted direct current. Devices of this character have been described by F A. W. Hull in an article entitled Hot cathode thyratrons in the General Electric Review, vol. 32, No. 2, April 1929, pages 2l3to 223 inclusive. The operating characteristics of these devices, such as their current-carrying capacity, also the maximum operating voltage, are determined to a large extent by the vapor pressure of the ionized medium and this in turn is a function, not only of the applied voltages andload currents, but also of the temperature surrounding the device. In order that the operation may be uniform over substantial periods of time under conditions of steady applied voltages, it is important that the devices, or rather certain portions of each envelope, be maintained at constant predetermined temperatures. These devices, when serving as control or relay units may in practice be positioned in places subject to large temperature variations, as for example, when they are presented alternately to sunlight and shadow, or to summer and winter conditions, so that unless the effects of these temperature variations are compensated,

the pressure of the vapor within the device will change and may seriously impair its electrical characteristics. The vapor condenses on the coolest portion of the envelope so that the temperature of this portion determines the amount of mercury 6 present within the tube in the form of vapor, hence, determines the degree of uniformity with which the tube operates. In accordance with my invention, I propose to regulate and control the temperature of the coolest portion of the tube even to the extent of having the temperature of this portion remain substantially constant, notwithstanding variable loadsand particularly variable temperature conditions surrounding the device as a whole, so that uniformity of operation under all conditions of ambient temperature is obtained. It will be understood that the temperature of any particular portion of the tube is dependent, not only upon the temperature of the surrounding medium, i. e. the room temperature, but also upon the heat generated in the tube due to load and cathode currents, all of which may be variable. I intend the terms ambient temperature and ambient condition as used in the specification and claims to include any or all of these effects and to refer to the temperature or condition respectively of that portion of the surrounding medium which is in the immediate vicinity of the tube and whose temperature is a direct function of that of the envelope. The improvement, essentially takes the form of an enclosure accessory in which the tube whose temperature is to be regulated, is inserted, said enclosure being provided with a door which is automatically opened when the temperature within the enclosure exceeds a predetermined value.

The invention will be better understood when reference is made to the following description in connection with the accompanying drawing in which Fig. 1 shows a view, partly in elevation and partly insection, of the improved temperature control accessory with a representative arc discharge device in place while Fig. 2 is a graph which depicts the improvement of operation when the tube is provided with the improved temperature regulating accessory.

Referring to Fig. 1, numeral 1 designates an arc discharge tube of conventional design whose temperature is to be maintained constant under conditions which normally would cause the temperature of the envelope to vary. This tube is positioned within a rectangular box 2 which may be of metal, asbestos or other suitable material, said box being substantially closed on all sides except for a large rectangular opening at the top the enclosure.

which is adapted to be closed by a swinging door or shutter 8. There are also one or more openings 4 at the bottom of two opposite sides of the box through which air or other fluid is admitted to The door is hung between two horizontal axes 5 and rests normally against a stop pin 6 in a closed position. The mechanism for opening the door consists of a thermostatic member '7 of any well lmown type, for example, a bimetallic strip, conveniently formed as a spiral in order to obtain the greatest length of strip in a relatively small space and secured to one of the sides of the box in any suitable manner, near the lower and coolest portion oi the are discharge device. There is a connecting rod 8 secured between the outer end of the thermostatic strip and a position on the door, removed from the swinging axis.

The normal cathode heat radiation of the arc discharge device maintains the enclosure, with the door closed, at a sufilciently high temperature in the coldest operating ambient condition. If desired, an additional heater may be employed to produce this result, although such a heater is generally unnecessary. As soon as the temperature within the enclosure rises above the desired value, the door 3 automatically opens in a gradual manner on account of the pressure exerted upwardly by the expansion of the thermostatic strip and assumes a position such that a draft oi? cooling fiuid sweeps in through the side openings and out through the top. The amount of fluid which reaches the device 1 in this manner is dependent upon the size of the opening at the top and hence, is a function of the amount of change produced in the metallic strip 7. When the desired temperature is reached within the box while the door is opening, the door comes to rest and stays in this open position so long as the temperature within the enclosure remains the same. However, when the temperature within the box becomes greater or less than the predetermined value, the door will assume new positions to allow corresponding changes of the draft eifect, until the desired temperature is again reached. The bimetallic strip member may be provided with an adjusting screw 9 which serves to adjust the position of the door in such a manner as it will begin to open when a predetermined temperature within the enclosure is reached. Inasmuch as the thermostatic strip is positioned near the cooler portion of the envelope, it is evident that the temperature regulation obtained in the manner described is under the exclusive control of the ambient conditions immediately surrounding that portion of the envelope whose temperature determines the vapor pressure within the tube. It is also apparent that the control of vapor pressure procured in this manner is obtained without the necessity of providing an additional source of heat other than that which may be necessary to obtain the correct normal temperature within the enclosure but is usually brought about solely by the heat generated within the device as well as the ambient heat. Consequently, the tube and its temperature regulating accessory constitute a self-contained, complete operating unit, and in operation, performs efiiciently.

Fig. 2 depicts a comparison of the operation of an arc discharge device provided, in the one case with the improved regulator, and in the'other case, without the regulator. In the graph, the curves are drawn between the temperature or the mercury vapor as ordinate, and the ambient temperature as abscissa. These curves clearly show that it is possible in a given installation, to maintain the temperature of the vapor, hence its pressure, substantially constant between a change in ambient temperature from 5 C. to approximately 30 C., a variation 01' more than 25 which would cover many of the temperature variations found in practice. It is evident that the range within which the temperature of the enclosure may be maintained constant, depends upon the amount of controlled cooling effect obtained by the movable door. This effect may of course, be increased by providing additional openings and doors operated from separate adjustable bimetallic strip members or a common member. It will also be noted from the graph, that the curve of the tube provided with the improved regulating device not only tends to become fiat, thus moving toward a condition of constant temperature but also actually crosses the operating curve of the tube not so provided, which fact indicates that it is feasible, by the improved arrangement, actually to cool the tube to a lower temperature when utilizing the regulator than would be possible in the absence of the regulator. This condition may be desirable in certain cases and is brought about by the continual draft eil'ect obtained by the cool fluid entering the side apertures and finding exit through the top opening in the enclosure when the door is operated.

While I have described my improved temperature regulator in connection with an arc discharge device employing condensable material for the ionized medium, it is evident that the invention is not limited thereto but finds general use in the electron tube art. The regulator has utility in connection with all sorts oi. vacuum tubes, for example, rectifiers and amplifiers, containing gas, with or without cumulative ionization, in all of which the temperature of the envelope as a whole or a certain portion thereof may be required to be maintained at a predetermined value, notwithstanding temperature changes in the ambient conditions. In the case of tubes which do not employ a condensable material, hence. in which the cooler portion or the envelope does not determine the pressure of the gaseous medium, the position of the bi-metallic strip may be such as to respond closely to the temperature of the envelope as a whole. The improved regulator will then serve to control the average temperature of the tube under conditions of variable loads and ambient temperatures.

The broader aspects or this invention are covered in the Hull application, Ser. No. 539,695, filed May 25, 1931, entitled "Thermostatic control for thermionic arc discharge devices and assigned to the same assignee as the present application.

What I claim as new and desire to secure by Letters Patent oi the United States is:

1. A temperature regulator for an electron discharge device, said regulator comprising an enclosure for the device and provided with an opening through which a temperature-controlling fluid is permitted to reach the device, and means for automatically regulating the size of the opening in response to changes in temperature of said device.

2. A temperature regulator for an electron discharge device, said regulator comprising an enclosure for the device and provided with an opening through which a temperature-controlling fluid is permitted to reach the device, and means for automatically regulating the size of the opening in response to changes in temperature of said device, said means comprising a member whose shape changes upon subjection to heat.

3. A temperature regulator for an electron discharge device, said regulator comprising an enclosure for the device and provided with an opening through which a temperature-controlling fluid is permitted to reach the device, and means for automatically regulating the size of the opening in response to changes in temperature of said device, said means comprising a member whose shape changes upon subjection to heat, said member being constituted of a bi-metallic strip and positioned near the base of said device.

4. A temperature regulator for an arc discharge device which employs a condensable material for the ionized medium, comprising an enclosure for the device provided with an opening through which air is permitted to reach the device, and means for automatically regulating the size of the opening in response to changes in ambient temperature whereby the temperature of the device and the vapor pressure of the condensable material are maintained substantially constant under variable ambient temperature conditions within the enclosure, said means comprising a thermostatic strip positioned near the portion of the envelope at which a substantial part of the vapor condenses.

5. In combination, an electron discharge device comprising an envelope containing cooperating electrodes and a condensable, ionizable material, a portion of which vaporizes under operating conditions and another portion remains in a condensed state in the coolest part of the envelope, means for maintaining a constant vapor pressure within the device under operating conditions, said means comprising an enclosure for the device provided with an opening through which temperature-controlling fluid is permitted to reach the portion of the envelope containing the condensed material, and means for automatically regulating the size of the opening in response to changes in temperature of said coolest envelope portion, said means including a thermostat positioned near said coolest envelope portion and responsive to temperature variations thereof.

JOHN H. PAYNE. 

